European television transmission standards provide for twenty-five frames, interlaced, per second. Each one of the frames is built up of two fields, interlaced with respect to each other, each one being scanned for the duration of 1/50 second. Each first field starts with line 1 of the TV standard scan and terminates for example in accordance with the CCIR standard, with line 3121/2. The CCIR standard provides 625 lines per frame. Each second field in the system starts with line 3121/2 and ends with line 625. Each field of each category is characterized by providing associated synchronizing signals. The necessary synchronism at any point of the overall transmission system is thereby insured. To maintain this synchronism, it is necessary that the alternating sequence of the first and second frame is retained, independently of the image or scene content.
Motion picture film is customarily recorded with a standard film speed of 24 images per second. Each image corresponds to a frame on the film. This film speed is retained also upon reproduction by motion picture projectors, so that the movement and course of scenes which were filmed is reproduced with precise time consistency. If motion picture films are to be reproduced on television operating according to the CCIR standard, or other standards which have 25 frames per second, it is possible to operate the film scanner slightly faster, so that the film in the scanner will run at a higher speed than 24 frames per second. This greatly simplifies the processing of the film in the scanner and in the recording instrument. The film speed coupled to the television system then will be 25 film frames per second. Each film frame is scanned twice, in order to obtain the requisite fields, with a different scanning track--to provide for the interlace; in accordance with some other apparatus, the film is scanned once and split electronically into the respective fields. The increased speed of reproduction, raised by the ratio of 25/24, results in slightly faster movement of moving events being reproduced; the increase is about 4%. In general, this is not noticeable to the viewer and is entirely tolerable. In this system, each television (TV) frame has the content of a motion picture frame and the transition from one film scene to a scene, for example from a different source, is accordingly possible after any one film frame. The associated audio cutting presents 25 possibilities per second for making a cut.
The situation becomes much more complicated when films, recorded at 24 frames per second, are to be reproduced in accordance with the NTSC standard, of 30 frames, that is, 60 fields per second. Increasing the film speed to 30 frames per second, or decreasing it to 15 frames per second, is not possible since the speed of movement portrayed, for example, on the film will become unrealistic. It has been proposed and has been in operation for many years to solve the problem by a 3/2 film feed in the film scanner.
In accordance with this prior art proposal, two sequential film frames are scanned in such a way that the first one is scanned three times and the second one is scanned twice. A third film frame is then again scanned three times and a fourth one twice. Each scanning is to obtain one TV field. The scanning of the first film frame of the sequence thus starts with the first field, continues with the second film field, and terminates with the endof the first field of the next TV frame. The next film frame is then scanned first with the scanning pattern of the second field and subsequently with that of the first field for the following third TV frame. The third film frame is again scanned three times in accordance with the TV standard, starting with the second field of the third TV full frame and terminating with the second field of the fourth TV full frame. The fourth film frame is scanned twice for the fifth TV frame. Consequently, after each four film frames, five TV frames will have been generated; with these four film frames and five TV frames, the sequence if terminated.
The ratio of four film frames to five TV frames corresponds exactly to the ratio of motion picture film speed to TV frame repetition rate (24:30). Similar conditions will result in film repetition rates which are a multiple or a fraction of standard speed of 24 frames per second.
Apparatus to scan motion picture images and to generate signals for recording the images on magnetic tape, in accordance with television standards, is usually referred to as telecine apparatus.
Problems arise due to the changing association between film frame and television scanned field when cutting, and particularly when cutting of video tape, is to be carried out. The publication "SMPTE Journal" November 1981, pp. 1085-1089, describes a system to generate a cutting list for TV treatment of films by magnetic tape, and which is concerned with the difficulties discussed above and suggests a solution. The known system requires transfer of a specific cutting code from the film scanner to the magnetic tape apparatus and recording thereof on the magnetic tape. This is a condition of proper operation. Recording does not comply with internationally set standards.